Summary Hospital-acquired infections due to various pathogens including P. aeruginosa (Pa) impose huge financial burdens in the USA. Development of effective therapeutics for infection has been hampered due to limited knowledge in infection targets. Studying the molecular mechanisms of alveolar macrophages (AM) in fighting Pa infection may help discover novel therapeutic approaches. Aautophagy is a mechanism by which cellular components are sequestered to autophagosomes for degradation through ubiquitination. We recently revealed that Pa infection can induce autophagy, and subsequently increasing bacterial degradation. Toll like receptors (TLRs) are implied in linking autophagy with macrophage phagocytosis. Interestingly, our preliminary data indicate that Lyn, interacting with TLR-2, plays a critical function in facilitating phagocytosis and bactericidal activity. Moreover, Lyn may also interact with Atg-7 during Pa infection. Finally, autophagy inhibitor 3-methyladenine (3MA) decreased phagocytosis and subsequent bacterial clearance by AM. Herein, we hypothesize that autophagy enhances phagocytic function, increases bacterial clearance, and lowers inflammatory responses. The objective of this proposal is to examine the physiological significance of autophagy in Lyn-Atg7- modulated phagocytosis in knockout (KO) mice, whose inflammatory responses may be suppressed leading to less tissue injury. Our long-term goal is to identify the mechanisms of AM defense against Pa invasion in order to design novel strategies to treat this infection. The rationale is that execution of this research will define autophagy as a novel defense mechanism against Pa infection, thus suggesting new therapeutic targets. With the strong basis of scientific data and other resources available, we are well positioned to test the following specific aims. Specific Aim 1: Dissect the effects of autophagy on Pa phagocytosis efficiency. We hypothesize that autophagy will increase bacterial clearance by influencing phagocytic function. Mice and primary AM cells will be used to study the role of autophagy in phagocytic cup formation and bacterial clearance. Specific Aim 2: Study the activity of Lyn in initiating and executing autophagic pathway. We hypothesize that Lyn, by transmitting TLR2 signals, is a key regulator in Pa-induced autophagy. Activation of this signaling pathway is expected to increase the formation and maturation of autophagosomes in a newly identified immunity mechanism to combat invading Pa in the host. Specific Aim 3: Identify the role of Atg-7 in alleviating inflammation in mice. We hypothesize that autophagy can control the inflammatory process, thereby limiting tissue damage of infected mice. Using a novel animal imaging that includes novel luminescent reagents, we will distinguish early inflammatory responses from late ones.